Apparatus and method for determining soft of softer handoff in mobile communication system

ABSTRACT

Apparatus and method for determining soft or softer handoff are described. The present invention includes the steps of comparing sectors in an active set to set values corresponding to the soft or softer handoff for the sectors, respectively in a base station, transmitting a first parameter for selecting cell switching parameters between the sectors neighboring each other in the active set to a mobile station wherein the set values for the respective sectors are included in the first parameter, generating values of a parameter PDCH_GROUP_IDENTIFIER corresponding to a packet data channel group identifier using the set values included in the first parameter, determining whether a serving sector and a target sector among the sectors are in the soft or softer handoff using the generated values of the parameter PDCH_GROUP_IDENTIFIER, and selecting the cell switching parameters accordingly.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/793,158, filed on Mar. 3, 2004, now U.S. Pat. No. 7,349,373, whichpursuant to 35 U.S.C. § 119(a), claims the benefit of earlier filingdate and right of priority to Korean Application No. P2003-23029 filedon Apr. 11, 2003, the contents of which are hereby incorporated byreference herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mobile communication system, and moreparticularly, to an apparatus and method for determining soft or softerhandoff on cell switching in a mobile communication system.

2. Discussion of the Related Art

In the world of cellular telecommunications, those skilled in the artoften use the terms 1G, 2G, and 3G. The terms refer to the generation ofthe cellular technology used. 1G refers to the first generation, 2G tothe second generation, and 3G to the third generation.

1G is used to refer to the analog phone system, known as an AMPS(Advanced Mobile Phone Service) phone systems. 2G is commonly used torefer to the digital cellular systems that are prevalent throughout theworld, and include CDMAOne, Global System for Mobile communications(GSM), and Time Division Multiple Access (TDMA). 2G systems can supporta greater number of users in a dense area than can 1G systems.

3G is commonly used to refer to the digital cellular systems currentlybeing developed. Recently, third-generation (3G) CDMA communicationsystems have been proposed including proposals, such as cdma2000 andW-CDMA. These 3G communication systems are conceptually similar to eachother with some significant differences.

A cdma2000 system is a third-generation (3G) wideband, spread spectrumradio interface system which uses the enhanced service potential of CDMAtechnology to facilitate data capabilities, such as Internet andintranet access, multimedia applications, high-speed businesstransactions, and telemetry. The focus of cdma2000, as is that of otherthird-generation systems, is on network economy and radio transmissiondesign to overcome the limitations of a finite amount of radio spectrumavailability.

FIG. 1 illustrates a wireless communication network architecture.

Referring to FIG. 1, a subscriber uses a Mobile Station to accessnetwork services. The Mobile Station may be a portable communicationsunit, such as a hand-held cellular phone, a communication unit installedin a vehicle, or even a fixed-location communications unit.

The electromagnetic waves from the Mobile Station are transmitted by theBase Transceiver System (BTS) also known as node B. The BTS consists ofradio devices such as antennas and equipment for transmitting radiowaves. The Base Station Controller (BSC) receives the transmissions fromone or more BTS's. The BSC provides control and management of the radiotransmissions from each BTS by exchanging messages with the BTS and theMobile Switching Center (MSC) or Internal IP Network. The BTS's and BSCare part of the Base Station (BS).

The BS exchanges messages with and transmits data to a Circuit SwitchedCore Network (CSCN) and Packet Switched Core Network (PSCN). The CSCNProvides traditional voice communications and the PSCN provides Internetapplications and multimedia services.

The Mobile Switching Center (MSC) portion of the CSCN provides switchingfor traditional voice communications to and from an Mobile Station andmay store information to support these capabilities. The MSC may beconnected to one of more BS's as well as other public networks, forexample a Public Switched Telephone Network (PSTN) or IntegratedServices Digital Network (ISDN). A Visitor Location Register (VLR) isused to retrieve information for handling voice communications to orfrom a visiting subscriber. The VLR may be within the MSC and may servemore than one MSC.

A user identity is assigned to the Home Location Register (HLR) of theCSCN for record purposes such as subscriber information, for exampleElectronic Serial Number (ESN), Mobile Directory Number (MDR), ProfileInformation, Current Location, and Authentication Period. TheAuthentication Center (AC) manages authentication information related tothe Mobile Station. The AC may be within the HLR and may serve more thanone HLR. The interface between the SC and the HLR/AC is an IS-41standard interface.

The Packet Data Serving Node (PDSN) portion of the PSCN provides routingfor packet data traffic to an from Mobile Station. The PDSN establishes,maintains, and terminates link layer sessions to the Mobile Station'sand may interface with one of more BS and one of more PSCN.

The Authentication, Authorization and Accounting (AAA) Server providesInternet Protocol authentication, authorization and accounting functionsrelated to packet data traffic. The Home Agent (HA) providesauthentication of MS IP registrations, redirects packet data to an fromthe Foreign Agent (FA) component of the PDSN, and receives provisioninginformation for users from the AAA. The HA may also establish, maintain,and terminate secure communications to the PDSN and assign a dynamic IPaddress. The PDSN communicates with the AAA, HA and the Internet via anInternal IP Network.

FIG. 2 illustrates a data link protocol architecture layer for awireless network.

Referring to FIG. 2, the upper layer contains three basis services;voice services 62, data services 61 and signaling 70. Voice services 62include PSTN access, mobile-to-mobile voice services, and Internettelephony. Data services 61 are services that deliver any form of dataon behalf of a mobile end user and include packet data applications(e.g., IP service), circuit data applications (e.g., asynchronous faxand B-ISDN emulation services), and SMS. Signaling 70 controls allaspects of mobile operation.

The Link Layer 30, is subdivided into the Link Access Control (LAC)sublayer 32 and the Medium Access Control (MAC) sublayer 31. The linklayer provides protocol support and control mechanisms for datatransport services and performs the functions necessary to map the datatransport needs of the upper levels 60 into specific capabilities andcharacteristics of the physical layer 20. The Link Layer 30 may beviewed as an interface between the upper layers and the Physical Layer20.

The separation of MAC 31 and LAC 32 sublayers is motivated by the needto support a wide range of upper layer services, and the requirement toprovide for high efficiency and low latency data services over a wideperformance range (from 1.2 Kbps to greater than 2 Mbps). Othermotivators are the need for supporting high QoS delivery of circuit andpacket data services, such as limitations on acceptable delays and/ordata BER (bit error rate), and the growing demand for advancedmultimedia services each service having a different QoS requirements.

The LAC sublayer 32 is required to provide a reliable, in-sequencedelivery transmission control function over a point-to-point radiotransmission link 42. The LAC sublayer manages point-to pointcommunication channels between upper layer entities and providesframework to support a wide range of different end-to-end reliable linklayer protocols.

The MAC sublayer 31 facilitates complex multimedia, multi-servicescapabilities of 3G wireless systems with Quality of Service (QoS)management capabilities for each active service. The MAC sublayer 31provides procedures for controlling the access of data services (packetand circuit) to the physical layer 20, including the contention controlbetween multiple services from a single user, as well as betweencompeting users in the wireless system. The MAC sublayer 31 alsoprovides for reasonably reliable transmission over the radio link layerusing a Radio Link Protocol (RLP) 33 for a best-effort level ofreliability. Signaling Radio Burst Protocol (SRBP) 35 is an entity thatprovides connectionless protocol for signaling messages. Multiplexingand Quality of Service (QoS) Control 34 is responsible for enforcementof negotiated QoS levels by mediating conflicting requests fromcompeting services and the appropriate prioritization of accessrequests.

The Physical Layer 20, is responsible for coding and modulation of datatransmitted over the air. The Physical Layer 20 conditions digital datafrom the higher layers so that the data may be transmitted over a mobileradio channel reliably.

The Physical Layer 20 maps user data and signaling, which are deliveredby the MAC sublayer 31 over multiple transport channels, into a physicalchannels and transmits the information over the radio interface. In thetransmit direction, the functions performed by the Physical Layer 20include channel coding, interleaving, scrambling, spreading andmodulation. In the receive direction, the functions are reversed inorder to recover the transmitted data at the receiver.

Generally, in the 1×EV-DV (1× Evolution-Data and Voice) system, when amobile station is in a soft or softer handoff area, a base stationtransmits packet data on forward-packet data channel (hereinafterabbreviated F-PDCH) in forward link from (or through) a serving sectoronly among various sectors in an active set. The active set is the listof pilots that are being used for the current communication. In otherwords, the active set is the list of sectors that are in communicationwith the mobile station.

If it is requested to switch the serving sector as the channel status orsignal power is changed, the serving sector is replaced by a sectorhaving the best status (or target sector), for example the strongestsignal power level. The data is then communicated between the mobilestation and the base station of the replaced target sector as a newserving sector. Such a procedure is called ‘cell switching’.

FIG. 3 is a diagram of determining and managing one serving sector in anactive set. Referring to FIG. 3, a mobile station measures strength of apilot signal from each sector in a neighbor set and tests whether themeasured signal meets certain requirements, such as the signal beinggreater than a certain threshold value (for example, T_ADD). If a resultof the test is acceptable, the terminal informs a base station ofinformation about the strength of the pilot signal of each of thecorresponding sectors through an extended pilot strength measurementmessage (EPSMM). The neighbor set is a set of sectors or pilots in thevicinity of the sectors currently transmitting to the mobile station.The contents of the neighbor set are normally configured by the basestation.

The base station uses the strength information of the received pilotsignal to determine the active set and then informs the mobile stationof the determined active set through, for example, a universal handoffdirection message. Conversely, the mobile station measures strength of apilot signal from each sector in the active set and tests whether themeasured strength is smaller than a predetermined threshold value (forexample, T_DROP). If the measured strength is smaller than thepredetermined threshold value T_DROP, the mobile station informs thebase station of information concerning the strength of the pilot signalof each corresponding sector in the active set through an extended pilotstrength measurement message (EPSMM). The base station uses the strengthinformation of the received signal to determine the correspondingsectors as an active set and then sends the active set through, forexample, the universal handoff direction message (UHDM). Generally, thesectors that are not included in the UHDM as the active set will beincluded in the neighbor set.

Moreover, the mobile station measures strength of the pilot signal ofeach sector in the active set for cell switching to select an optimalsector as a serving sector and then informs the base station of thedetermined serving sector through a channel quality indicator (CQI)cover of a reverse channel quality indicator channel (R-CQICH).

If the CQI cover received through the R-CQICH indicates a sector of itsown, the corresponding sector recognizes to be selected as the servingsector and starts transmission of the packet data accordingly.

FIG. 3 illustrates an example of sector 1 being selected as a servingsector. FIG. 4 illustrates an example of cell switching.

Referring to FIG. 4, a mobile station is receiving packet data 1, packetdata 2, and packet data 3 through sector 2, which is a current servingsector. If sector 3 is designated as a new serving sector since statusof channel R-CQICH is changed, the mobile station should direct thesector 3 with the CQI cover. The sector 3 used as the serving sectorthen receives packet data 4 from a base station controller (BSC) andtransmits the received packet data to the mobile station.

As mentioned in the foregoing explanation, in order to perform the cellswitching correctly in the mobile communication network, an efficientmethod is needed to judge that the corresponding cells/sectors for thecell switching lie in what kind of handoff areas, respectively. However,the related art fails to propose any method of having the base stationor mobile station judge the areas efficiently.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method ofdetermining soft or softer handoff on cell switching in a mobilecommunication system that substantially obviates one or more problemsdue to limitations and disadvantages of the related art.

An object of the present invention is to provide a method of determiningsoft or softer handoff on cell switching in a mobile communicationsystem having a base station and a terminal, by which it is able toefficiently determine cell-switching-related sectors lie in what kind ofhandoff areas, respectively on cell switching.

Another object of the present invention is to provide a method ofdetermining soft or softer handoff on cell switching in a mobilecommunication system, which enables a mobile communication network or aterminal to efficiently determine soft or softer handoff on cellswitching.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, amethod of cell switching in a mobile communication system comprises thesteps of determining an active set comprising at least one sector beinga serving sector; receiving from a network, preferably through auniversal handoff direction message, a control parameter (PWR_COMB_INDor PDCH_GROUP_IND) for each sector in the active set, the controlparameter being associated with using at least one of first-type (soft)and second-type (softer) handoff when transitioning from the servingsector to a target sector; determining in the mobile station identifierparameters (PDCH_GROUP_IDENTIFIER) corresponding to the sectors in theactive set, each identifier parameter being determined by associatingcontrol parameters of at least two sectors in the active set (forexample, PDCH_GROUP_IDENTIFIER is set to previous value if nextPDCH_GROUP_IND is set to “1”); determining in the mobile station atleast one of the first-type and the second-type handoff by comparing atleast two identifier parameters corresponding to the sectors in theactive set; and selecting cell switching parameters corresponding to atleast one of the first-type and the second-type handoff.

According to one aspect of the present invention, the control parametersis determined by using one sector of the active set as a reference andcomparing other sector in the active set to determine whether theseneighboring sectors are with the same cell, wherein a cell comprises atleast one sector. The control parameter preferably comprises a powercombining indicator if a packet data channel group indicator is notreceived from the network.

According to another aspect of the present invention, the step ofdetermining the identifier parameters further comprises: comparing thecontrol parameter of one sector to next sector in the active set so thatif the control parameter of the next sector is at a first logic level(if PDCH_GROUP_IND=1) then the corresponding identifier parameter is setto previous identifier parameter, and if the control parameter of thenext sector is at a second logic level (if PDCH_GROUP_IND=0) then thecorresponding identifier parameter is increase by a predetermined value(by one) from the previous identifier parameter. The identifierparameter corresponding to a first sector in the active set is set to apredetermined value (for example “000”).

According to another aspect of the present invention, the step ofdetermining the identifier parameters further comprises: setting a nextidentifier parameter to the identifier parameter of previous sector inthe active set that supports the packet data communication, ifcorresponding control parameter is set to a first level and there are noother sectors between a present sector corresponding to the nextidentifier parameter and a previous sector that support the packet datacommunication; setting the identifier parameter to the identifierparameter of previous sector in the active set that supports the packetdata communication, if corresponding control parameter is set to a firstlevel and all sectors between the present sector corresponding to thenext identifier parameter and a previous sector in the active set thatsupport packet data communication have corresponding control parameterset to the first level; and otherwise set the identifier parameter to avalue different (for example, one greater) than the identifier parametercorresponding to previous sector that supports the data packetcommunication in the active set.

According to still another aspect of the present invention, the step ofdetermining the first-type and second-type handoff further comprises:comparing the identifier parameter of the serving sector to the targetsector in the active set so that if both identifier parameters aredifferent then the first-type handoff is recognized for the mobileterminal to transition from the serving sector to the target sector, andif both identifier parameters are the same, then the second-type handoffis recognized.

In another embodiment of the present invention, a mobile station for usein a mobile communication system comprises an antenna; a processor forcontrolling the mobile station; a display in communication with theprocessor to display user interface information; a keyboard incommunication with the processor to input user controlled data. Theprocessor comprises means for receiving a control parameter for eachsector in the active set, the control parameter being associated withusing at least one of first-type (soft) and second-type (softer) handoffwhen transitioning from the serving sector to a target sector; means fordetermining identifier parameters (PDCH_GROUP_IDENTIFIER) correspondingto the sectors in the active set, each identifier parameter beingdetermined by associating control parameters of at least two sectors inthe active set (for example, PDCH_GROUP_IDENTIFIER is set to previousvalue if next PDCH_GROUP_IND is set to “1”); means for determining atleast one of the first-type and the second-type handoff by comparing atleast two identifier parameters corresponding to the sectors in theactive set; and means for selecting cell switching parameterscorresponding to at least one of the first-type and the second-typehandoff.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 illustrates a wireless communication network architecture.

FIG. 2 illustrates the data link protocol architecture for a wirelessnetwork.

FIG. 3 illustrates an exemplary diagram of determining and managing oneserving sector in an active set.

FIG. 4 illustrates an example of cell switching.

FIG. 5 illustrates a reverse channel quality indicator channel (R-CQICH)during cell switching from serving sector A to target sector B accordingto one embodiment of the present invention.

FIG. 6 illustrates cell switching diagram, more particularly, withrespect to the soft and softer handoffs.

FIG. 7 is a flowchart for determining parameter PDCH_GROUP_IDENTIFIERcorresponding to a packet data channel group identifier when the numberof active sets is ‘N’.

FIG. 8 illustrates a flow chart for determining the parameterPDCH_GROUP_IDENTIFIER when not all sectors in the active set supportpacket data channel (PDCH).

FIG. 9 is a flowchart for determining whether serving and target sectorsare in soft or softer handoff relationship according to the preferredembodiment of the present invention.

FIG. 10 illustrates a block diagram of mobile station according to thepreferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts. To aiddescribing the present invention, certain parameter names are being usedto describe the channels, messages and variables communicated betweenmobile and base stations. It should be noted that such parameter namesare for illustration purposes only, and that other names may be used todescribe the same or similar function.

FIG. 5 illustrates a reverse channel quality indicator channel (R-CQICH)during cell switching from serving sector A to target sector B accordingto an embodiment of the present invention.

Referring to FIG. 5, a frame length of R-CQICH is preferably 20 ms andis constructed with 16 slots. In normal state instead of cell switchingstate, each of the slots of the frame transmits measured channel statusinformation to a mobile station.

In the embodiment of the present invention, a first slot denoted by ‘0’expresses the measured channel status information by 4-bits to transmitto the mobile station, and each of the subsequent slots 1˜15 expresseswhether a channel status of the current slot is better (UP) or worse(DOWN) than that of the previous slot by 1-bit to transmit to the mobilestation. Namely, a differential measurement (DM) is performed on eachslot.

In this embodiment, all slots in the frame use the CQI cover as anidentifier indicating a current serving sector. In the cell switchingstate, an UP command is always issued for last Ns (number of switchingslots) slots of each channel frame regardless of the channel status andthe corresponding slots use the CQI cover indicating the target sector(i.e. a sector to be a subsequent serving sector). Such a procedure isrepeated for Nf (number of channel frames for cell switching) frames.

‘Ns’ and ‘Nf’ used for the cell switching procedure vary according towhether the corresponding sectors are related to the soft handoff or thesofter handoff. In case of the soft handoff, parameterNUM_SOFT_SWITCHING_SLOTS corresponding to the number of soft switchingslots is used as the Ns and parameter NUM_SOFT_SWITCHING_FRAMEScorresponding to the number of soft switching frames is used as the Nf.In case of the softer handoff, parameter NUM_SOFTER_SWITCHING_SLOTScorresponding to the number of softer switching slots is used as the Nsand parameter NUM_SOFTER_SWITCHING_FRAMES corresponding to the number ofsofter switching frames is used as the Nf.

In determining the cell switching parameters, the mobile station needsanother parameter of time required for the handoff. Such a time variesin accordance with the soft handoff or the softer handoff as well. Incase of the soft handoff, a parameter corresponding to a soft switchingdelay number NUM_SOFT_SWITCHING_DELAY is used. Alternatively, during asofter handoff, a parameter corresponding to a softer switching delaynumber NUM_SOFTER_SWITCHING_DELAY is used.

For example, the parameters, such as NUM_SOFT_SWITCHING_SLOTS,NUM_SOFTER_SWITCHING_SLOTS, NUM_SOFT_SWITCHING_FRAMES,NUM_SOFTER_SWITCHING_FRAMES, NUM_SOFT_SWITCHING_SLOTS_CHM,NUM_SOFTER_SWITCHING_SLOTS_CHM, NUM_SOFT_SWITCHING_FRAMES_CHM,NUM_SOFTER_SWITCHING_FRAMES_CHM, NUM_SOFT_SWITCHING_DELAY, andNUM_SOFTER_SWITCHING_DELAY, depend on the handoff information which istransmitted to the mobile station through a channel assignment message,such as the ECAM (extended channel assignment message), and a handoffmessage, such as the UHDM (universal handoff direction message), and areselectively used for the cell switching in the mobile station.

The parameters NUM_SOFT_SWITCHING_SLOTS_CHM,NUM_SOFTER_SWITCHING_SLOTS_CHM, NUM_SOFT_SWITCHING_FRAMES_CHM, andNUM_SOFTER_SWITCHING_FRAMES_CHM are preferably used in case that theterminal is in control hold mode.

The use of soft or softer handoff related parameters are generallydictated upon determination by mobile station which type of handoff touse transitioning from a serving sector to a target sector. Therefore,the correct determination of soft or softer handoff according to apreferred embodiment of the present invention is explained in detail.

The base station, through a down link message, such as universal handoffdirection message, provides the mobile station information pertaining towhether to use soft or softer handoff. Such handoff information may bebased on a power combining indicator (PWR_COMB_IND), or alternatively, apacket data channel group indicator (PDCH_GROUP_IND), if packet data issupported in the communication network. In the network, the actualparameter may be used for more than one purpose. For example, thePWR_COMB_IND also indicates whether or not to combine power control bitsfor one or more sectors.

However, using such handoff information some times provides incorrecthandoff instruction. FIG. 6 illustrates cell switching diagram, moreparticularly, with respect to the soft and softer handoffs. For example,referring to FIG. 6, the mobile station is located in the shaded area155. Hence, the active set comprises sectors A, B and C. Let's assumethat sector A is a serving sector and is the first one in the active setlist. The base station compares sectors (also referred to as pilots) inthe active set to each other to set a value corresponding to softhandoff or softer handoff for each sector.

When determining soft or softer handoff, there may exist inconsistencybetween MAC and Signaling layers in the operation of PDCH_GROUP_IND.

In the MAC layer, if a target sector (for example, Sector B in FIG. 6)is not in the active set but a current sector (for example, Sector A inFIG. 6) is in the active set, the mobile (or base) station performs thefollowing: If the PDCH_GROUP_IND field corresponding to the targetsector is equal to the PDCH_GROUP_IND field corresponding to the currentsector, the mobile (or base) station sets NUM_SWITCHING_FRAMES toNUM_SOFTER_SWITCHING_FRAMES and sets NUM_SWITCHING_SLOTS toNUM_SOFTER_SWITCHING_SLOTS. Otherwise, the mobile (or base) station setsNUM_SWITCHING_FRAMES to NUM_SOFT_SWITCHING_FRAMES and setsNUM_SWITCHING_SLOTS to NUM_SOFT_SWITCHING_SLOTS.

In the Signaling layer, if PDCH_GROUP_IND_INCL is set to ‘0’, the basestation omits this field; otherwise, the base station includes thisfield and sets it as follows.

If the mobile station is to use the softer reselection parameters whenre-pointing between this pilot and the previous pilot in this message,the base station sets this field to ‘1’. If the mobile station is to usethe soft reselection parameters when re-pointing between this pilot andthe previous pilot in this message, the base station sets this field to‘0’. The base station sets this field to ‘0’ in the first record in thepilot list.

The respective set values for the sectors, which are included in a firstparameter (or field) PDCH_GROUP_IND corresponding to a packet datachannel group indication for determining cell switching parametersbetween neighbor sectors in the active set and a second parameter (orfield) PWR_COMB_IND corresponding to a power combination indication forindicating whether power control bits between the neighbor sectors inthe active set are combined or not, are transmitted to the mobilestation. Receiving the first parameter PDCH_GROUP_IND from the basestation, the mobile station generates values of a parameterPDCH_GROUP_IDENTIFIER corresponding to a packet data channel groupidentifier using each of the values which are set by the base station tobe included in the fields, respectively.

If the first parameter PDCH_GROUP_IND is not supported by the basestation, the mobile station generates values of the parameterPDCH_GROUP_IDENTIFIER corresponding to the packet data channel groupidentifier using the values included in the second parameterPWR_COMB_IND.

Subsequently, the mobile station determines whether the serving andtarget sectors are in soft or softer handoff using the generated valuesof the parameter PDCH_GROUP_IDENTIFIER, and then selects the parametersfor the cell switching according to a result of the determination.

Preferably, relating to distinction between the soft handoff and thesofter handoff, the base station may transmit both the parametersPDCH_GROUP_IND and PWR_COMB_IND to the mobile station through the ECAM(extended channel assignment message) and the UHDM (universal handoffdirection message). Alternatively, the base station may only support theparameter PWR_COMB_IND.

The first parameter PDCH_GROUP_IND is preferably a 1-bit parameter usedfor determining the parameters for the cell switching between theneighboring sectors in the active set. A value of the 1-bit for thefirst sector of the list in the active set is ‘0’. After the firstsector, if a subsequent sector compared to a previous sector is in thesoft handoff relation, the 1-bit is set to ‘0’. If the subsequent sectoris in the softer handoff relation, the 1-bit is set to ‘1’.

The second parameter PWR_COMB_IND is preferably a 1-bit parameter usedfor indicating whether power control bits between the neighboringsectors in the active set are combined or not. A value of the 1-bit forthe first sector of the list in the active set is ‘0’. After the firstsector, if a subsequent sector compared to a previous sector is in thesoft handoff relation, the 1-bit is set to ‘0’. If the subsequent sectoris in the softer handoff relation, the 1-bit is set to ‘1’. In case thatthe first parameter PDCH_GROUP_IND is not received from the basestation, the second parameter PWR_COMB_IND can be used in determiningthe cell switching parameters.

According to the preferred embodiment of the present invention, a thirdparameter PDCH_GROUP_IDENTIFIER is newly defined and used in the mobilestation to further carry out the determination of the soft or softerhandoff between two sectors of one or more cells. The parameterPDCH_GROUP_IDENTIFIER represents packet data group identifierinformation, and is preferably 3 bits long.

The mobile station uses the values of the received first or secondparameter PDCH_GROUP_IND or PWR_COMB_IND to determine whether thecorresponding sectors are in the soft or softer handoff relation andthen determines the cell switching parameters.

FIG. 7 is a flowchart for determining parameter PDCH_GROUP_IDENTIFIERwhen all sectors in the active set supports, for example, packet datachannel (PDCH). The determination of the parameter PDCH_GROUP_IDENTIFIERis preferably performed in the signaling layer of the mobile station.

Referring to FIG. 7, the mobile station first determines whether thefirst parameter PDCH_GROUP_IND is received from the base station (S250).If the first parameter PDCH_GROUP_IND is received, the mobile stationthen determines whether the sector being examined is the first sector inthe active set. If the corresponding sector is the first sector in theactive set, the value of the parameter PDCH_GROUP_IDENTIFIER(1) is setto a predetermined value, preferably ‘000’ (S270). If the correspondingsector is not the first sector in the active set, the value of the firstparameter PDCH_GROUP_IND(i) of the corresponding sector (assuming thatit is an i^(th) sector in the active set) is examined. If the value ofPDCH_GROUP_IND(i) is, for example, ‘1’, then the value of the parameterPDCH_GROUP_IDENTIFIER(i) is determined to be equal to that of (i−1)^(th)parameter PDCH_GROUP_IDENTIFIER(i−1) (S260). If the value ofPDCH_GROUP_IND(i) is, for example, ‘0’, then the value of the parameterPDCH_GROUP_IDENTIFIER(i) is ‘1’ greater than that of parameterPDCH_GROUP_IDENTIFIER(i−1) (S265). In other words, PDCH_GROUP_IDENTIFIER(i) is set to PDCH_GROUP_IDENTIFIER (i−1)+1.

If the first parameter PDCH_GROUP_IND is not received from the basestation, the mobile station determines whether the corresponding sectoris the first sector or not. If the corresponding sector is the firstsector, the value of the parameter PDCH_GROUP_IDENTIFIER(1) is set to‘000’ (S290). If the corresponding sector is not the first sector, thevalue of the second parameter PWR_COMB_IND(i) of the correspondingsector is examined (S275). If the value of PWR_COMB_IND(i) is, forexample, ‘1’, the value of the parameter PDCH_GROUP_IDENTIFIER(i) isdetermined to be equal to that of (i−1)^(th) parameterPDCH_GROUP_IDENTIFIER(i−1) (S280). If the value of PWR_COMB_IND(i) is,for example, ‘0’, the value of the parameter PDCH_GROUP_IDENTIFIER(i) is1 greater than that of parameter PDCH_GROUP_IDENTIFIER(i−1) (S285). Inother words, PDCH_GROUP_IDENTIFIER (i) is set to PDCH_GROUP_IDENTIFIER(i−1)+1.

The above process is best explained by an example. It is assumed thatthe sectors in the active set are A1, A2, B2, and C3, that the sectorsA1 and A2 are in the softer handoff relation, and that the rest of thesectors are in the soft handoff relation. In this case, values of thefirst or second parameters PDCH_GROUP_IND or PWR_COMB_IND can bedetermined using Expression 1.PDCH_GROUP_IND(A1)=0,PDCH_GROUP_IND(A2)=1,PDCH_GROUP_IND(B2)=0,PDCH_GROUP_IND(C3)=0 orPWR_COMB_IND(A1)=0,PWR_COMB_IND(A2)=1,PWR_COMB_IND(B2)=0,PWR_COMB_IND(C3)=0  [Expression 1]

If the parameter PDCH_GROUP_IDENTIFIER comprises with three bits, valuesof the parameter PDCH_GROUP_IDENTIFIER can be represented by Expression2.PDCH_GROUP_IDENTIFIER(A1)=‘000’PDCH_GROUP_IDENTIFIER(A2)=‘000’PDCH_GROUP_IDENTIFIER(B1)=‘001’PDCH_GROUP_IDENTIFIER(C3)=‘010’  [Expression 2]

Once the values of the parameter PDCH_GROUP_IDENTIFIER for the sectorsof the active set are determined, the mobile station may determinewhether the serving and target sectors related to the cell switching arein the soft or softer handoff relation according to the determinedvalues of the parameter PDCH_GROUP_IDENTIFIER.

FIG. 8 illustrates a flow chart for determining the parameterPDCH_GROUP_IDENTIFIER when not all sectors in the active set supportpacket data channel (PDCH).

Referring to FIG. 8, in the event that not all sectors (also referred toas “pilots” since the active set is a list of pilots) in the active setsupport the packet data, the first sector in the list that has a PDCHassignment, the mobile station sets PDCH_GROUP_IDENTIFIER to ‘000’ asshown in S310 of FIG. 8. Otherwise, the mobile station performs thefollowing: If PDCH is assigned for this pilot (sector) and ifPWR_COMB_IND is set to ‘1’ (S320), and there are no pilots between thispilot and the previous pilot in the list that has a PDCH assigned(S315), the mobile station sets PDCH_GROUP_IDENTIFIER to the same valueas that of the previous pilot in the list that has a F-PDCH assigned(S340). Otherwise, the mobile station sets PDCH_GROUP_IDENTIFIER to thevalue one greater than that of the previous pilot in the list (S345).

If PWR_COMB_IND is set to ‘1’ (S330), and all pilots between this pilotand the previous pilot in the list that has a F-PDCH assigned havePWR_COMB_IND set to ‘1’ (S325), the mobile station setsPDCH_GROUP_IDENTIFIER to the same value as that of the previous pilot inthe list that has a F-PDCH assigned (S350). Otherwise, the mobilestation sets PDCH_GROUP_IDENTIFIER to the value one greater than that ofthe previous pilot in the list that has a F-PDCH assigned (S355).

FIG. 9 is a flowchart for determining whether serving and target sectorsare in soft or softer handoff relation using values of a packet datachannel group identifier parameter PDCH_GROUP_IDENTIFIER in the mobilestation. The determination of the whether the soft or softer handoffshould be used based on the value of the parameterPDCH_GROUP_IDENTIFIER(i) is preferably made in the MAC layer of themobile station.

Referring to FIG. 9, the mobile station compares a value of theparameter PDCH_GROUP_IDENTIFIER(serving sector) to that of the parameterPDCH_GROUP_IDENTIFIER(target sector). If they are equal, it isdetermined that the serving and target sectors are in the softer handoffrelation. If they fail to be equal, it is determined that the servingand target sectors are in the soft handoff relation.

As mentioned in the foregoing description, if it is determined that theserving and target sectors are in the soft handoff relation, the mobilestation uses a parameter NUM_SOFT_SWITCHING_SLOTS corresponding to thesoft switching slot number, a parameter NUM_SOFT_SWITCHING_FRAMEScorresponding to the soft switching frame number, a parameterNUM_SOFT_SWITCHING_SLOTS_CHM corresponding to the soft switching slotnumber in a control hold mode, a parameter NUM_SOFT_SWITCHING_FRAMES_CHMcorresponding to the soft switching frame number in the control holdmode, and a parameter NUM_SOFT_SWICHING_DELAY corresponding to the softswitching delay number as the cell switching parameters.

If it is determined that the serving and target sectors are in thesofter handoff relation, the mobile station uses a parameterNUM_SOFTER_SWITCHING_SLOTS corresponding to the softer switching slotnumber, a parameter NUM_SOFTER_SWITCHING_FRAMES corresponding to thesofter switching frame number, a parameterNUM_SOFTER_SWITCHING_SLOTS_CHM corresponding to the softer switchingslot number in a control hold mode, a parameterNUM_SOFTER_SWITCHING_FRAMES_CHM corresponding to the softer switchingframe number in the control hold mode, and a parameterNUM_SOFTER_SWICHING_DELAY corresponding to the softer switching delaynumber as the cell switching parameters.

Accordingly, in the present invention, the new parameter namedidentifier PDCH_GROUP_IDENTIFIER is defined, which facilitates todetermine whether the related sectors are in the soft or softer handoffrelation using the parameter values. Therefore, the present inventionenables to efficiently select the cell switching parameters.

FIG. 10 illustrates a block diagram of mobile station according to thepreferred embodiment of the present invention.

Referring to FIG. 10, the mobile station 500 comprises a processor (ordigital signal processor) 510, RF module 535, power management module505, antenna 540, battery 555, display 515, keypad 520, memory 530, SIMcard 525 (which may be optional), speaker 545 and microphone 550.

A user enters instructional information, such as a telephone number, forexample, by pushing the buttons of a keypad 520 or by voice activationusing the microphone 550. The microprocessor 510 receives and processesthe instructional information to perform the appropriate function, suchas to dial the telephone number. Operational data may be retrieved fromthe Subscriber Identity Module (SIM) card 525 or the memory module 530to perform the function. Furthermore, the processor 510 may display theinstructional and operational information on the display 515 for theuser's reference and convenience.

The processor 510 issues instructional information to the RF section535, to initiate communication, for example, transmit radio signalscomprising voice communication data. The RF section 535 comprises areceiver and a transmitter to receive and transmit radio signals. Anantenna 540 facilitates the transmission and reception of radio signals.Upon receiving radio signals, the RF module 535 may forward and convertthe signals to baseband frequency for processing by the processor 510.The processed signals would be transformed into audible or readableinformation outputted via the speaker 545, for example.

It will be apparent to one skilled in the art that the preferredembodiments of the present invention can be readily implemented using,for example, the processor 510 or other data or digital processingdevice, either alone or in combination with external support logic.

The preferred embodiments may be implemented as a method, apparatus orarticle of manufacture using standard programming and/or engineeringtechniques to produce software, firmware, hardware, or any combinationthereof. The term “article of manufacture” as used herein refers to codeor logic implemented in hardware logic (e.g., an integrated circuitchip, Field Programmable Gate Array (FPGA), Application SpecificIntegrated Circuit (ASIC), etc.) or a computer readable medium (e.g.,magnetic storage medium (e.g., hard disk drives, floppy disks, tape,etc.), optical storage (CD-ROMs, optical disks, etc.), volatile andnon-volatile memory devices (e.g., EEPROMs, ROMs, PROMs, RAMs, DRAMs,SRAMs, firmware, programmable logic, etc.). Code in the computerreadable medium is accessed and executed by a processor. The code inwhich preferred embodiments are implemented may further be accessiblethrough a transmission media or from a file server over a network. Insuch cases, the article of manufacture in which the code is implementedmay comprise a transmission media, such as a network transmission line,wireless transmission media, signals propagating through space, radiowaves, infrared signals, etc. Of course, those skilled in the art willrecognize that many modifications may be made to this configurationwithout departing from the scope of the present invention, and that thearticle of manufacture may comprise any information bearing medium knownin the art.

The logic implementation shown in the figures described specificoperations as occurring in a particular order. In alternativeimplementations, certain of the logic operations may be performed in adifferent order, modified or removed and still implement preferredembodiments of the present invention. Moreover, steps may be added tothe above described logic and still conform to implementations of theinvention.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present invention. Thus,it is intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A method of cell switching in a mobile communication systemcomprising at least one base station, each base station corresponding toone-or-more sectors, the method performed by the at least one basestation comprising: setting an identifier parameter associated with afirst sector in an active set to ‘000’; setting a next identifierparameter to the identifier parameter of previous sector in the activeset that supports the packet data communication, if correspondingcontrol parameter is set to a first level (‘1’) and there are no othersectors between a present sector corresponding to the identifierparameter and a previous sector that support the packet datacommunication; setting the identifier parameter to the identifierparameter of previous sector in the active set that supports the packetdata communication, if corresponding control parameter is set to a firstlevel (‘1’) and all sectors between the present sector corresponding tothe next identifier parameter and a previous sector in the active setthat support packet data communication have corresponding controlparameter set to the first level; and otherwise set the identifierparameter to a value different than the identifier parametercorresponding to previous sector that supports the data packetcommunication in the active set.
 2. The method of claim 1, furthercomprising setting the identifier parameter corresponding to a firstsector in the active set to a predetermined value.